holokrine

Holocrine secretion is a mode of exocrine secretion in which mature secretory cells accumulate product and then rupture, releasing their contents and dying. The released material, together with cellular debris from the disintegrating cells, forms the secretory product in the gland lumen. Replacement of lost secretory cells occurs from stem cells in the gland’s basal layer, maintaining the secretory tissue.

Mechanistically, secretory cells enlarge as they synthesize and store lipids, proteins, or other secretory products. At the end of their life cycle, the entire cell disintegrates, contributing its cytoplasmic contents to the secretion. This contrasts with merocrine secretion, where cells remain intact and release products via exocytosis, and with apocrine secretion, where only a portion of the cell apex is lost with cytoplasm.

Holocrine secretion is most famously associated with sebaceous glands of the skin, which produce sebum. Sebocytes fill with lipid-rich material, then rupture to release oil that coats hair and skin. Similar holocrine processes occur in other glands where the secretory cells become part of the secretory mixture through disintegration.

Etymology: from Greek holos “whole” and krinein “to separate” or “to secrete.” In practice, the term is used in histology to distinguish holocrine glands from merocrine and apocrine glands.

Clinical notes: abnormal holocrine activity can affect skin health, with overproduction or defective turnover of sebaceous glands contributing to conditions such as acne. In histological sections, holocrine secretion may be identified by the presence of lipid droplets and remnants of dead secretory cells within the gland lumen.